1. Field of the Invention
The invention relates to the use of organofunctionally modified polysiloxanes containing phenyl derivatives as dispersants and wetting agents for fillers and pigments in aqueous pigment pastes and/or ink and paint formulations. For the purposes of this invention the term “polysiloxanes” shall be understood to embrace oligomeric siloxanes as well.
2. Background of the Invention
For the dispersing of fillers and pigments in liquid media the assistance of dispersants is necessary for a variety of reasons and is therefore state of the art:                improved wetting of the fillers and pigments during incorporation, resulting for example in shorter dispersing times and lower input of dispersing energy;        reduced viscosity of the pigment pastes or of inks and paints, allowing more efficient dispersion to give more highly concentrated pastes;        development of optimum color strength and also of optimum hiding power in the case of opaque pigments;        development of high degrees of gloss particularly in aqueous dispersions drying by means of coalescence;        prevention of the settling tendency in pigment pastes during months of storage, in transit over long distances, and under extreme climatic stress, as must be guaranteed in the case of pigments with a high density such as titanium dioxide, for example;        avoidance of flocculation, particularly important for ensuring reproducible shades in the color mixing machines which are nowadays customary,        realization of compatibility with a large number of binders used for let down.        
In order to meet these diverse requirements imposed on dispersants both during the preparation and in the storage period of pastes, inks, and paints a multiplicity of water-soluble dispersant structures have already been proposed.
In addition to the use of inexpensive ionic structures particularly for fillers and oxide pigments based on polyphosphates (Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, section 3.2.6., 2002; Th. Staffel, Farbe & Lack 100, 1994) and polyacrylic acids (WO-A-02/14415, WO-A-01/60925, J. Schröder, Farbe & Lack 91, 1985, 11; R. Hildred, Farbe & Lack, 1990, 857–859) a broad sphere of application in the production of inks and paints has been occupied by amphiphilic structures based on nonionic fatty alcohol ethoxylates or alkylphenol ethoxylates and/or their anionically modified derivatives (J. Bieleman, PPCJ 3, 1995, 17; P. Quednau, ACT '98, Paper No. 29; H. Frommelius, VILF (German Paint and Ink Engineers Association) 2000 Annual Conference, 41).
A substantial disadvantage of the first-mentioned structures is their suitability solely for oxide pigments but not for hydrophobic organic pigments. Another drawback is the inadequate long-term stability of the pastes produced using them and the heavy dependence of the viscosities on the use concentration and electrolyte concentration, which may vary not only through the introduction of charges by different pigments but also through the use of the water which is customary in the manufacture of pastes, inks, and paints.
In principle these last-mentioned problems also occur in connection with the ionic fatty alcohol or alkylphenol ethoxylate (APE) derivatives, which also tend toward strong foam stabilization, resulting not only in production problems but also, in many cases, in a reduced gloss.
The nonionic derivatives which are suitable for organic pigments frequently exhibit inadequate affinity and viscosity reduction for oxide pigments.
Although alkylphenol ethoxylates offer better pigment wetting and greater permanence than conventional linear or branched fatty alcohols, their ecotoxicology is increasingly imposing pressure for them to be substituted in the inks and paints industry (Journal of Surfactants and Detergents, Vol. 5, No. 1, (2002); Critical reviews in Toxicology, 26(3):335–364, (1996); P. Schöberl, Tenside Surfactants Detergents 25, 1988, 2, 86; K. Fent, Swiss Federal Institute for Environmental Science and Technology).
There have without doubt been a multiplicity of efforts to find a response to the requirements of dispersants by means of polymeric structures.
Descriptions are given, for example, of water-soluble polyiso-cyanate adducts containing hydrophilic polyether chains (EP-A-0 731 148), hydrophilic polyurethane-polyureas (DE-A-44 16 336), poly(meth)acrylates (U.S. Pat. No. 3,980,602, WO-A-94/21701), and also special polyesters (WO-A-94/18260) or else copolymers based on vinyl monomers (styrene, vinylimidazole, etc.) with acrylate-functional monomers (acrylic acid, BuAc, HEA), as in EP-B-0 311 157.
As well as disruptive or even toxic residual monomer fractions there is frequently no universal compatibility with the typical binder systems.
Owing to molar weight, monomers, or long polyethylene oxide chains, which are needed for water solubility, the resultant products are frequently solid and by neutralization can generally be formulated only as 40% strength aqueous solutions, thereby restricting the user in the production of highly concentrated pastes.
A strong inherent color on the part of amino-containing polymers or the adverse influencing of water resistance and/or weathering stability in pigmented inks and paints is an additional restriction on the use of such structures.
A further serious disadvantage lies in the relatively large amounts that are required of polymeric structures particularly for titanium dioxide—one of the most frequently used pigments.
The effectiveness of polymeric structures in terms of long-term paste stability as a result of polyfunctional anchor possibilities is countered by high production costs, arising from the polymerization and possible polymer-analogous reactions.
From DE-C-41 40 793, EP-A-0 546 407, and EP-A-0 546 406 it is known that silicone oils and also silane-based structures such as methacryloyloxypropyltrimethoxysilane (VILF, volume 3, Annual Conference November 2000; 6th Nuremberg Congress, p 147 ff., April 2001) are capable of coating even oxide surfaces in order to produce greater compatibility with the surrounding organic medium, by making the surface water repellent and reducing the viscosity, and so to guarantee greater efficiency of the pigments employed.
Generally speaking, however, the pigments in question are those which are used in plastics applications, such as for the production of pigment masterbatches in polyethylene or polypropylene.
In ink and paint applications silanes are utilized for modifying inorganic materials in order to make the polar surfaces, which are the cause of particle agglomeration and high viscosity in an organic system, of the appropriate organofunctional silanes sufficiently organophilic and so to improve the wetting afforded by the organic polymer (Degussa brochure “Anwendung von organofunktonellen Silanen—DYNASYLAN”). Silicas treated in this way are employed in UV-curing systems, which are fundamentally different from these aqueous applications.